Is it possible to float an object on a fluid simulation?
In short, no. But...

This part of the wiki talks a little about setting an object as an inlet, outlet, obstacle, or fluid control. There are also settings in the fluid sim that tries to imitate foam floating on the surface of the fluid, but there's not a way to make an object float, per se. Nor will the fluid sim interact with a rigid body.

That being said, it's possible to export a fluid sim to a mesh, in which case it will have the same attributes as any other mesh. Not quite interaction, but close.